In additive fabrication processes with high imaging resolution, an object can be built layer-by-layer by use of a foil to transport a layer of build material and position the layer in contact with a previously formed layer of an object in an object building area where the layer is hardened by radiation from an exposure unit to form the newly hardened layer of the object. The object is held by an object carrier. The previously formed layer may not be completely hardened when the newly hardened layer is formed. Prior to forming the subsequent layer, the foil can be separated from the newly hardened layer by peeling the foil from the newly hardened layer of the object. The force applied to peel the foil from the newly hardened layer must be large enough to overcome the adhesive force between the foil and the newly hardened layer. However, it is critical that the newly hardened layer is not separated from the previously formed layer during the peeling process.
Additive fabrication processes that utilize a foil to transport build material to an object build area and peel the foil from the newly hardened layer are known. For example, U.S. Pat. No. 6,547,552 to Fudim (the '552 patent) uses a roller assembly and foil to contact a layer of build material to a previously formed layer of an object. An exposure unit exposes the layer to radiation to harden the layer and adhere the hardened layer to the previously formed layer of the object. The roller assembly moves back toward to its original position to peel the foil from the newly hardened layer of the object. This process is repeated to create subsequent layers of the object until the object is completed. Similarly, U.S. Pat. No. 7,731,887 to Hull et al. (the '887 patent) discloses foil based additive fabrication process where a roller is used to peel foil from a newly hardened layer of an object.
EP2011631A1 to Envisiontec GmbH discloses the sensing of certain build conditions in order to affect several process parameters in a system wherein a foil is in contact with build material contained in a vat. The disclosed process parameters that may be affected include tilting of the object carrier and/or the foil in order to create an angle between the newly hardened layer of an object and the building plane. The creation of this angle allegedly has the effect of enhancing or adjusting separation forces. However, this method is cumbersome and requires displacement of the entire object carrier or entire foil. Moreover, since the build material useful in such processes is often highly flowable, tilting of the entire foil may cause spills, undesirable buildup of build material in some areas, or increase in the time of equilibration of the build material in the vat.
U.S. Pat. No. 7,614,866 to 3D Systems discloses a method of foil-based additive fabrication. The cured resin is separated from the foil primarily by a shearing action, but the elevator platform can be titled to facilitate removal.
An apparatus and method for additive fabrication which prevents the newly hardened layer from being separated from the previously formed layer of the object while the foil is peeled from the newly hardened layer by controlling or reducing the separation forces is thus desirable.